I have a 2008 300 hp Optimax 2 stroke outboard. The trim sender on the lower unit is for a digital (smartcraft) guage. My boat builder installed analog guages. Should I be able to hook up a digital depth finder with the analog guages or do I need to change out the digital sending unit to analog?

Analog guages do not work with digital sending units. There are certain models of SmarCraft guages that have analog needles and they look analog but are actually digital.

Just gotta make sure you know exactly what you have.